Zymocin-induced DNA damage is lethal in the yeast Saccharomyces cerevisiae.
Tammy Westmoreland, John Olson, William Saito, Jeffrey Marks, Craig Bennett
Dept. of Surgery, Duke University Medical Center, 355 MSRB, Durham, NC, 27710, USA
Secretion of the heterotrimeric toxin zymocin by Kluyveromyces lactis inhibits the growth of other yeast species including Saccharomyces cerevisiae. Although this protein toxin affects transcription in susceptible yeast, little is known about its lethal mode of action. Here we show that diploid yeast strains defective in the repair of ionizing radiation (IR) induced double-strand breaks (DSBs) including members of the RAD52, RAD6 and RAD9 epistasis groups have enhanced sensitivity to the killing effects of zymocin. Furthermore, IR sensitive mutant strains that are defective in transcriptional regulation and/or replication such as ccr4 or mms22 strains show extreme hypersensitivity to the killing effects of zymocin. Following exposure to zymocin, most unbudded ccr4 and mms22 cells rapidly transit G1 and S phases to permanently arrest in G2 as budded cells which undergo lysis. This S/M checkpoint arrest is similar to that induced by the replication inhibitor hydroxyurea which is consistent with zymocin acting as an S phase specific replication inhibitor. Similar to IR-induced DSB damage, recombination proficient diploid cells were much more resistant to the killing effects of zymocin than haploid cells. Moreover, we show that zymocin exposure induced transcription of a DIN::LacZ reporter construct (an indirect assay of DNA damage) in repair proficient yeast. Therefore zymocin-induced lethality appears to result from persistent DSB damage in the yeast S. cerevisiae.
Return to YGM 2004 Home at SGD